This invention is directed to jet engines and, more particularly, to thrust reversal control systems for fan jet engines.
Contemporary commercial and military jet aircraft are designed such that their jet engines are supported in positions ahead of, and below, the wings of the aircraft. Various types of thrust reversal control systems have been proposed for use with such engine/wing configurations. Some such thrust reversal control systems only control fan air during thrust reversal and provide no control over primary air. In such systems, the primary air exhausted under the wing during thrust reversal causes heating and sooting of the under-the-wing area. Heating and sooting, which cause corrosion and increase the rate of material deterioration, require the inclusion of special corrosion resistant and high temperature materials in these areas. In addition, an uncontrolled exhaust plume emitted under the wings during a thrust reversal mode of operation creates ground effect lift by daming the airflow under the wings and increasing pressure under the wing that tends to unload the landing gear and reduce the effect of the aircraft's brakes. Further, damage to the engine may be caused by the ingestion of the exhaust plume, causing engine surge, and ingestion of blown-up ground debris.
In order to alleviate the foregoing problems, the prior art has proposed the inclusion of primary air exhaust spoilers and thrust reverser deflectors. These devices are adapted to spoil and/or direct primary air away from under-the-wing areas. Such devices have met with only limited success in directing hot exhaust gasses away from the aircraft structure and off the runway. While some of these devices have assisted in reducing heat corrosive damage and sooting of the under wing area, adverse ground effect lift and under wing aerodynamic daming problems still exist. In this regard, an engine thrust reverser plume emitted under the wing has the adverse effect of reducing the time period that reversers can be operated during landing roll out. Also, a low profile exhaust plume causes inlet injestion surge, injestion of runway debris and prevents the wing flaps from aerodynamically braking the aircraft.
Therefore, it is an object of this invention to provide a new and improved primary exhaust thrust reversal vectoring control system.
It is a further object of this invention to provide a new and improved primary exhaust control system that substantially reduces heat corrosive damage and sooting of the underwing area of an aircraft during thrust reversal.
It is also an object of this invention to provide a fan and primary exhaust control system that produces zero or very low landing gear unloading thru ground effects caused by under wing exhaust plumes that aerodynamically dam the air under the wing.
Another disadvantage of prior art thrust reversal control systems that control primary air as well as fan air relates to their requirement for individual control mechanisms. More specifically, in the past, particularly prior to the introduction of long duct fan jet engines, one mechanism was used to control fan air and another was used to control primary air. With respect to fan air, usually a ring-shaped portion of the engine nacelle is translated rearwardly to expose cascade vanes. During this rearward movement, fan air duct blocker doors close the fan air duct aft of the cascade vanes to prevent fan air from exhausting rearwardly, whereby the fan air is exhausted in a thrust reversal direction via the cascade vanes. With respect to primary air, usually thrust spoilers or reversers located on the aft end of the engine are moved to primary air control positions. These devices, as noted above spoil and/or deflect primary air. Obviously, two control systems, one for controlling the direction of travel of fan air and another for controlling the direction of travel of primary air during thrust reversal are more complicated and heavier than a single control system. Complexity increases unreliability and weight reduces aircraft payload.
Therefore, it is also an object of this invention to provide combination primary and fan air thrust reversal control mechanisms.
It is another object of this invention to provide combination primary and fan air thrust reversal control mechanisms for long duct fan jet engines.
It is a still further object of this invention to provide thrust reversal control mechanisms for jet engines wherein the direction of flow of fan and primary air during thrust reversal is controlled by a common control mechanism.
It is a still further object of this invention to provide a combination primary and fan air thrust reversal control mechanism that uses primary air as well as fan air for thrust reversal.